Polymer electrolyte membrane, membrane electrode assembly comprising polymer electrolyte membrane and fuel cell comprising membrane electrode assembly

ABSTRACT

The present specification provides a polymer electrolyte membrane, a membrane electrode assembly including the polymer electrolyte membrane, and a fuel cell including the membrane electrode assembly.

TECHNICAL FIELD

The present specification claims priority to and the benefits of KoreanPatent Application No. 10-2013-0047773, filed with the KoreanIntellectual Property Office on Apr. 29, 2013, Korean Patent ApplicationNo. 10-2013-0049424, filed with the Korean Intellectual Property Officeon May 2, 2013, Korean Patent Application No. 10-2013-0132160, filedwith the Korean Intellectual Property Office on Nov. 1, 2013, and KoreanPatent Application No. 10-2013-0144440, filed with the KoreanIntellectual Property Office on Nov. 26, 2013, the entire contents ofwhich are incorporated herein by reference.

The present specification provides a polymer electrolyte membrane, amembrane electrode assembly including the polymer electrolyte membrane,and a fuel cell including the membrane electrode assembly.

BACKGROUND ART

A fuel cell is a high efficiency power generating device, and hasadvantages in that the amount of fuel use is low due to high efficiencycompared to existing internal combustion engines, and it is apollution-free energy source that does not produce environmentalpollutants such as SO_(x), NO_(x), VOC and the like. In addition, thereare additional advantages in that a locational area required forproduction facilities is small, and a construction period is short.

Accordingly, a fuel cell has a variety of applications covering a mobilepower supply such as portable devices, a transport power supply such asvehicles, and dispersion power generation usable for domestic use andelectric power industries. Particularly, when an operation of a fuelcell vehicle, a next generation transportation device, iscommercialized, the potential market size is expected to be extensive.

A fuel cell is largely divided into 5 types depending on the operatingtemperature and the electrolyte, which specifically includes an alkalifuel cell (AFC), a phosphoric acid fuel cell (PAFC), a molten carbonatefuel cell (MCFC), a solid oxide fuel cell (SOFC), a polymer electrolytemembrane fuel cell (PEMFC) and a direct methanol fuel cell (DMFC). Amongthese, a polymer electrolyte membrane fuel cell and a direct methanolfuel cell having excellent mobility have received wide attention as afuture power supply.

A polymer electrolyte membrane fuel cell has a basic principle such thatgas diffusing electrode layers are disposed on both surfaces of apolymer electrolyte membrane, and water is produced by a chemicalreaction through the polymer electrolyte membrane by facing an anodetoward a fuel electrode and a cathode toward an oxidation electrode, andthe reaction energy produced therefrom is converted to electric energy.

A typical example of an ion-conducting polymer electrolyte membrane mayinclude Nafion, a perfluorinated hydrogen ion exchange membranedeveloped by Dupont USA in early 1960s. Similar commercializedperfluorinated polymer electrolyte membranes other than Nafion includeAciplex-S membrane manufactured by Asahi Kasei Chemicals Corporation,Dow membrane manufactured by Dow Chemical Company, Flemion membranemanufactured by Asahi Glass Co., Ltd., and the like.

Existing commercialized perfluorinated polymer electrolyte membrane haschemical resistance, oxidation resistance, and excellent ionconductance, but has a problem of being expensive and causingenvironmental problems due to the toxicity of intermediates producedduring manufacture. Accordingly, polymer electrolyte membranes in whicha carboxyl group, a sulfonic acid group or the like is introduced to anaromatic ring polymer have been studied in order to compensate for theweaknesses of such perfluorinated polymer electrolyte membranes.Examples thereof include sulfonated polyarylether sulfone [Journal ofMembrane Science, 1993, 83, 211], sulfonated polyetherether ketone[Japanese Patent Application Laid-Open Publication No. H06-93114, U.S.Pat. No. 5,438,082], sulfonated polyimide [U.S. Pat. No. 6,245,881] andthe like.

A polymer electrolyte membrane accompanies changes in membranethicknesses and volumes of 15 to 30% depending on the temperature andthe degree of hydration, and accordingly, the electrolyte membrane isrepeatedly expanded and contracted depending on the operation conditionof a fuel cell, and microholes or cracks occur due to such volumechanges. In addition, as a side reaction, hydrogen peroxide (H₂O₂) orperoxide radicals are generated from a reduction reaction of oxygen in acathode, which may cause the degradation of the electrolyte membrane. Apolymer electrolyte membrane for a fuel cell has been developed in thedirection of improving mechanical and chemical durability keeping such aphenomenon that may occur during the fuel cell driving in mind.

Studies that have been carried out for improving mechanical durabilityinclude a reinforcing composite electrolyte membrane prepared byintroducing a Nafion solution (5% by weight concentration) to an e-PTFE(U.S. Pat. No. 5,547,551), and a polymer blend composite membraneintroducing a polymer having excellent dimensional stability to asulfonated hydrocarbon-based polymer material (Korean Patent No.10-0746339), and the like. In addition, W.L. Gore & Associatesintroduces a reinforcing composite electrolyte membrane productcommercialized as a trade name of Gore Select.

In a reinforcing composite electrolyte membrane, a porous support isused in order to provide mechanical properties and dimensionalstability. A porous support needs to maintain mechanical durabilitywhile not declining the performances, therefore, a support made ofsuitable materials provided with high porosity and excellent mechanicalproperties needs to be selected. In addition, ion conductivity of amembrane greatly varies depending on the method of immersing an ionconductor into a support and the type of the ion conductor, therefore,development of an effective method of immersing an ion conductor, and anion conductor suitable for a reinforcing composite electrolyte membranehas been required.

DISCLOSURE Technical Problem

An object of the present specification is to provide a polymerelectrolyte membrane, and moreover, to provide a membrane electrodeassembly including the polymer electrolyte membrane, and a fuel cellincluding the membrane electrode assembly.

Technical Solution

One embodiment of the present specification provides a polymerelectrolyte membrane including a mixed layer that includes an ionmigration region and a support having a 3-dimensional network structure,wherein the ion migration region has a structure in which two or morecells including a hydrocarbon-based ion-conducting material border 3dimensionally, and an RH cycle limit is at least 20,000 cycles.

One embodiment of the present specification provides a polymerelectrolyte membrane including a mixed layer that includes an ionmigration region and a support having a 3-dimensional network structure,wherein the ion migration region has a structure in which two or morecells including a hydrocarbon-based ion-conducting material border 3dimensionally, and a maximum stress in a machine direction (MD) of thepolymer electrolyte membrane is 200 kgf/cm² or greater.

One embodiment of the present specification provides a polymerelectrolyte membrane including a mixed layer that includes an ionmigration region and a support having a 3-dimensional network structure,wherein the ion migration region has a structure in which two or morecells including a hydrocarbon-based ion-conducting material border 3dimensionally, and a maximum stress in a vertical direction of a machinedirection (MD) of the polymer electrolyte membrane is 200 kgf/cm² orgreater.

One embodiment of the present specification provides a membraneelectrode assembly including the polymer electrolyte membrane.

One embodiment of the present specification provides a fuel cellincluding the membrane electrode assembly.

Advantageous Effects

A polymer electrolyte membrane according to one embodiment of thepresent specification has an advantage of having excellent durability.Specifically, using a membrane electrode assembly including the polymerelectrolyte membrane according to one embodiment of the presentspecification in a fuel cell may contribute to performance enhancementof the fuel cell. In other words, a polymer electrolyte membraneaccording to one embodiment of the present specification minimizesperformance decline of a fuel cell in the working environment of thefuel cell in which high temperature humidification and drying arerepeated leading to the repetition of contraction and expansion of apolymer electrolyte membrane, and allows the fuel cell to maintainsteady performance.

DESCRIPTION OF DRAWINGS

FIGS. 1 and 2 are diagrams showing one region of a surface of a polymerelectrolyte membrane according to one embodiment of the presentspecification.

FIG. 3 is a diagram showing one region of a section of a polymerelectrolyte membrane according to one embodiment of the presentspecification.

FIG. 4 is a diagram showing a structure of a fuel cell according to oneembodiment of the present specification.

FIG. 5 shows measurement results of maximum diameters of the surfacecells of a polymer electrolyte membrane according to one embodiment ofthe present specification.

FIG. 6 shows RH cycle results according to examples and comparativeexamples.

FIG. 7 shows a voltage depending on current density of a membraneelectrode assembly prepared according to Test Example 2.

BEST MODE

Hereinafter, the present specification will be described in more detail.

In the present specification, a description of one member being placed“on” another member includes not only a case of the one member adjoiningthe another member but a case of still another member being presentbetween the two members.

In the present specification, a description of a certain part“including” certain constituents means capable of further includingother constituents, and does not exclude other constituents unlessparticularly stated on the contrary.

One embodiment of the present specification provides a polymerelectrolyte membrane including a mixed layer that includes an ionmigration region and a support having a 3-dimensional network structure,wherein the ion migration region has a structure in which two or morecells including a hydrocarbon-based ion-conducting material border 3dimensionally, and an RH cycle limit is at least 20,000 cycles.

According to one embodiment of the present specification, the polymerelectrolyte membrane may have an RH cycle limit of at least 40,000cycles.

In addition, according to one embodiment of the present specification,the polymer electrolyte membrane may have an RH cycle limit of at least50,000 cycles.

Furthermore, according to one embodiment of the present specification,the polymer electrolyte membrane may have an RH cycle limit of at least60,000 cycles.

In addition, according to one embodiment of the present specification,the polymer electrolyte membrane may have an RH cycle limit of at least70,000 cycles.

Furthermore, according to one embodiment of the present specification,the polymer electrolyte membrane may have an RH cycle limit of at least75,000 cycles.

In addition, according to one embodiment of the present specification,the polymer electrolyte membrane may have an RH cycle limit of at least80,000 cycles.

Furthermore, according to one embodiment of the present specification,the polymer electrolyte membrane may have an RH cycle limit of at least100,000 cycles.

In addition, according to one embodiment of the present specification,the polymer electrolyte membrane may have an RH cycle limit of at least120,000 cycles.

Furthermore, according to one embodiment of the present specification,the polymer electrolyte membrane may have an RH cycle limit of at least150,000 cycles.

According to one embodiment of the present specification, the polymerelectrolyte membrane hardly experiences performance decline in theabove-mentioned RH cycle range.

According to one embodiment of the present specification, the polymerelectrolyte membrane may have an RH cycle limit of 300,000 cycles orless.

According to one embodiment of the present specification, the polymerelectrolyte membrane may have an RH cycle limit of 500,000 cycles orless.

The polymer electrolyte membrane according to one embodiment of thepresent specification has an advantage of having excellent durability.Specifically, excellent durability of the polymer electrolyte membranemay be identified through an RH cycle. More specifically, the polymerelectrolyte membrane according to one embodiment of the presentspecification has an advantage in that durability decline caused byvolume changes that occur while conducting an RH cycle similar to a fuelcell driving condition is significantly small.

The RH cycle of the present specification means measuring durability ina fuel cell state after preparing the polymer electrolyte membrane as amembrane electrode assembly (MEA). Specifically, the RH cycle in thepresent specification means measuring durability under a condition of80° C. while injecting nitrogen to an anode at a flow rate of 0.95 slm(standard liter per minute), injecting nitrogen to a cathode at a flowrate of 1.0 slm, and switching between humidification of RH (relativehumidity) 150% and non-humidification of RH 0% at an interval of twominutes.

Moreover, the RH cycle of the present specification being higher means apolymer electrolyte membrane having higher durability. In addition, theRH cycle limit means the number of cycles up to the cycle at which apolymer electrolyte membrane is damaged enough to be unusable as an MEAfrom conducting the RH cycle.

In order to measure the RH cycle limit in the present specification,linear sweep volta-mmetry (LSV) is used. Specifically, the LSV meansmeasuring hydrogen crossover at 0.1 to 0.4 V (2 mV/s) while injectinghydrogen to an anode at a flow rate of 0.2 slm, and injecting nitrogento a cathode at a flow rate of 0.2 slm. In other words, when thehydrogen crossover value increases during the RH cycle, a polymerelectrolyte membrane may be considered to be damaged, and depending onthe degree of the hydrogen crossover value increase, the degree of thepolymer electrolyte membrane damage may be determined. When a hydrogencrossover value rapidly increases during the RH cycle, the polymerelectrolyte membrane is damaged enough not to perform its role, and thenumber of the RH cycles at the time may be the RH cycle limit.

For example, the RH cycle limit means the number of RH cycles duringwhich the hydrogen crossover value of a polymer electrolyte membranecapable of normal operation increases by 5 or more times.

In other words, the RH cycle having a higher limit means a polymerelectrolyte membrane having higher durability, and when the RH cyclelimit is at least 20,000 cycles, a polymer electrolyte membrane isgenerally considered to have excellent durability. The polymerelectrolyte membrane according to one embodiment of the presentspecification is capable of maintaining steady performance with almostno performance decline even when the RH cycle limit is 20,000 cycles orgreater.

According to one embodiment of the present specification, a maximumstress in the machine direction (MD) of the polymer electrolyte membranemay be 200 kgf/cm² or greater.

According to one embodiment of the present specification, a maximumstress in the vertical direction of the machine direction (MD) of thepolymer electrolyte membrane may be 200 kgf/cm² or greater.

One embodiment of the present specification provides a polymerelectrolyte membrane including a mixed layer that includes an ionmigration region and a support having a 3-dimensional network structure,wherein the ion migration region has a structure in which two or morecells including a hydrocarbon-based ion-conducting material border 3dimensionally, and a maximum stress in the machine direction (MD) of thepolymer electrolyte membrane is 200 kgf/cm² or greater.

One embodiment of the present specification provides a polymerelectrolyte membrane including a mixed layer that includes an ionmigration region and a support having a 3-dimensional network structure,wherein the ion migration region has a structure in which two or morecells including a hydrocarbon-based ion-conducting material border 3dimensionally, and a maximum stress in the vertical direction of themachine direction (MD) of the polymer electrolyte membrane is 200kgf/cm² or greater.

According to one embodiment of the present specification, the polymerelectrolyte membrane may have directivity. Specifically, according toone embodiment of the present specification, the support may be preparedthrough monoaxial orientation or biaxial orientation of a polymer, andthe support directivity caused by the orientation may determine thedirectivity of the polymer electrolyte membrane. Accordingly, thepolymer electrolyte membrane according to one embodiment of the presentspecification may have directivity of the machine direction (MD), anddirectivity of the vertical direction of the machine direction (MD), andthe polymer electrolyte membrane may exhibit differences in physicalproperties such as stress and elongation depending on the directivity.

The machine direction (MD) may have a meaning generally used in the art.Specifically, the machine direction may mean a winding direction whenprepared by being wound in a roll form.

According to one embodiment of the present specification, a maximumstress in the machine direction (MD) of the polymer electrolyte membranemay be 300 kgf/cm² or greater.

According to one embodiment of the present specification, a maximumstress in the machine direction (MD) of the polymer electrolyte membranemay be 500 kgf/cm² or greater.

According to one embodiment of the present specification, a maximumstress in the machine direction (MD) of the polymer electrolyte membranemay be 800 kgf/cm² or greater.

According to one embodiment of the present specification, a maximumstress in the machine direction (MD) of the polymer electrolyte membranemay be 900 kgf/cm² or greater.

According to one embodiment of the present specification, a maximumstress in the vertical direction of the machine direction (MD) of thepolymer electrolyte membrane may be 300 kgf/cm² or greater.

According to one embodiment of the present specification, a maximumstress in the vertical direction of the machine direction (MD) of thepolymer electrolyte membrane may be 400 kgf/cm² or greater.

According to one embodiment of the present specification, a maximumstress in the vertical direction of the machine direction (MD) of thepolymer electrolyte membrane may be 600 kgf/cm² or greater.

According to one embodiment of the present specification, a maximumstress in the vertical direction of the machine direction (MD) of thepolymer electrolyte membrane may be 800 kgf/cm² or greater.

According to one embodiment of the present specification, a maximumelongation in the machine direction (MD) of the polymer electrolytemembrane may be 20% or greater.

According to one embodiment of the present specification, a maximumelongation in the machine direction (MD) of the polymer electrolytemembrane may be 50% or greater.

According to one embodiment of the present specification, a maximumelongation in the machine direction (MD) of the polymer electrolytemembrane may be 60% or greater.

According to one embodiment of the present specification, a maximumelongation in the vertical direction of the machine direction (MD) ofthe polymer electrolyte membrane may be 10% or greater.

According to one embodiment of the present specification, a maximumelongation in the vertical direction of the machine direction (MD) ofthe polymer electrolyte membrane may be 30% or greater.

The maximum stress in the present specification means a magnitude offorce per unit area in the instant of a polymer electrolyte membrane cutwith a distance between grips of 100 mm and a tension speed of 10 mm/minunder a condition of a temperature of 20° C. and humidity of 22%.

In addition, the maximum elongation in the present specification means apercentage of polymer electrolyte membrane stretching in the instant ofthe polymer electrolyte membrane cut with a distance between grips of100 mm and a tension speed of 10 mm/min under a condition of atemperature of 20° C. and humidity of 22%. Specifically, the maximumstress and the maximum elongation in the present specification meansmeasuring a polymer electrolyte membrane cut in the form of a dog boneaccording to the American Society for Testing and Materials (ASTM)standard at a speed of 10 mm/min using a united test machine (UTM). TheUTM is an apparatus simultaneously measuring tensile strength andelongation, and is an apparatus generally used in the art.

The polymer electrolyte according to one embodiment of the presentspecification has a high maximum stress, therefore, has an advantage ofperforming its function for a long period of time without performancevariations in a fuel cell in which an electrolyte membrane is repeatedlyexpanded and contracted due to the repetition of high temperaturehumidification and drying.

According to one embodiment of the present specification, thehydrocarbon-based material is a polymer having one or more cationexchangers on the side chain, the ratio of the number of carbon atomsand the number of fluorine atoms included in the polymer is greater thanor equal to 1:0 and less than 1:1, and the cation exchanger may includeone or more types selected from the group consisting of a sulfonic acidgroup, a carboxylic acid group, a phosphoric acid group, a phosphonicacid group and derivatives thereof.

According to one embodiment of the present specification, thehydrocarbon-based material may not include fluorine on the main chain orside chain.

According to one embodiment of the present specification, the ratio ofthe number of carbon atoms and the number of fluorine atoms included inthe polymer may be greater than or equal to 1:0 and less than or equalto 2:1 in the hydrocarbon-based material.

According to one embodiment of the present specification, theion-conducting material may include a cation-conducting material and/oran anion-conducting material.

According to one embodiment of the present specification, theion-conducting material may include a proton conducting material.

According to one embodiment of the present specification, theion-conducting material may include one, two or more types selected fromthe group consisting of a sulfonated benzimidazole-based polymer, asulfonated polyimide-based polymer, a sulfonated polyetherimide-basedpolymer, a sulfonated polyphenylenesulfide-based polymer, a sulfonatedpolysulfone-based polymer, a sulfonated polyethersulfone-based polymer,a sulfonated polyetherketone-based polymer, a sulfonatedpolyether-etherketone-based polymer, a sulfonatedpolyphenylquinoxaline-based polymer, and a polymer in which a sulfonatedpartial fluorine-based is introduced.

According to one embodiment of the present specification, the polymer inwhich a sulfonated partial fluorine-based is introduced may be a polymerin which a sulfone group binds to at least one side chain, and the ratioof the number of carbon atoms and the number of fluorine atoms includedin the polymer is greater than 1:0 and less than 1:1.

According to one embodiment of the present specification, theion-conducting material may have ion conductance of 1 mS/cm or greaterat 60° C. or higher.

According to one embodiment of the present specification, theion-conducting material may have ion exchange capacity (IEC) of 1 meq/gor greater.

According to one embodiment of the present specification, the supportmay include a hydrocarbon-based material. Specifically, according to oneembodiment of the present specification, the support may be ahydrocarbon-based support.

According to one embodiment of the present specification, the supportmay include a semi-crystalline polymer.

The semi-crystalline polymer of the present specification may have acrystallinity range of 20% to 80%.

According to one embodiment of the present specification, thesemi-crystalline polymer may include polyolefin, polyamide, polyester,polyacetal (or polyoxymethylene), polysulfide, polyvinyl alcohol,copolymers thereof and combinations thereof, but is not limited thereto.

According to one embodiment of the present specification, the supportmay include those derived from polyolefin-based materials.

The polyolefin may include polyethylene (LDPE, LLDPE, HDPE, UHMWPE),polypropylene, polybutene, polymethylpentene, copolymers thereof andblends thereof.

The polyamide may include polyamide 6, polyamide 6/6, nylon 10/10,polyphthalamide (PPA), copolymers thereof and blends thereof, but is notlimited thereto.

The polyester may include polyester terephthalate (PET), polybutyleneterephthalate (PBT), poly-1-4-cyclohexylenedimethylene terephthalate(PCT), polyethylene naphthalate (PEN) and liquid crystal polymers (LCP),but is not limited thereto.

The polysulfide includes polyphenyl sulfide, polyethylene sulfide,copolymers thereof and blends thereof, but is not limited thereto.

The polyvinyl alcohol includes ethylene-vinyl alcohol, copolymersthereof and blends thereof, but is not limited thereto.

The polymer electrolyte membrane according to one embodiment of thepresent specification may include cells having uniform sizes.

Specifically, according to one embodiment of the present specification,an average of the maximum diameters of the cells may be greater than orequal to 0.25 μm and less than or equal to 0.4 μm. In addition,according to one embodiment of the present specification, a standarddeviation of the maximum diameters of the cells may be greater than orequal to 0.05 μm and less than or equal to 0.2 μm.

FIG. 5 shows measurement results of the maximum diameters of the surfacecells of the polymer electrolyte membrane according to one embodiment ofthe present specification. Specifically, FIG. 5 shows a maximum diameterof each cell located on the surface of the polymer electrolyte membraneaccording to one embodiment of the present specification, and shows afrequency of the maximum diameter of each cell after measuring themaximum diameters. Accordingly, it can be seen that the polymerelectrolyte membrane according to one embodiment of the presentspecification includes cells having uniform sizes.

According to one embodiment of the present specification, the cells maybe laminated in two or more layers in any one direction (x-axisdirection), a direction vertical thereto (y-axis direction), and athickness direction of the polymer electrolyte membrane (z-axisdirection) on any surface horizontal to the upper surface of the polymerelectrolyte membrane.

According to one embodiment of the present specification, the supportmay have a sponge structure in which two or more of the cells aredistributed.

According to one embodiment of the present specification, sections oftwo or more of the cells may be included in both the vertical sectionand the horizontal section of the polymer electrolyte membrane.

The diameter of the cell section of the present specification may meanthe length of the longest line crossing the cell section.

According to one embodiment of the present specification, the cellsection on the horizontal surface of the polymer electrolyte membranemay have a height to width ratio of 1:1 to 5:1.

According to one embodiment of the present specification, the cellsection on the vertical surface of the polymer electrolyte membrane mayhave a height to width ratio of 1:1 to 10:1.

According to one embodiment of the present specification, the diametersize of the cell section on the horizontal surface of the polymerelectrolyte membrane may be greater than or equal to 40 nm and less thanor equal to 1,000 nm.

According to one embodiment of the present specification, the diametersize of the cell section on the vertical surface of the polymerelectrolyte membrane may be greater than or equal to 40 nm and less thanor equal to 1,000 nm.

According to one embodiment of the present specification, the ratio ofthe cell numbers per 100 μm² of the horizontal surface and the verticalsurface of the polymer electrolyte membrane may be from 1:1 to 1:5.

According to one embodiment of the present specification, a variation inthe cell numbers on the vertical section and the horizontal section per100 μm² of the polymer electrolyte membrane may be greater than or equalto 0 and less than or equal to 500.

According to one embodiment of the present specification, an averagesize of the diameters of the cell sections may be greater than or equalto 40 nm and less than or equal to 500 nm.

According to one embodiment of the present specification, a standarddeviation of the diameters of the cell sections may be from 50 nm to 200nm.

According to one embodiment of the present specification, the celldiameters may be greater than or equal to 40 nm and less than or equalto 1000 nm.

According to one embodiment of the present specification, the support isformed with two or more nodes, and each node may include three or morebranches.

According to one embodiment of the present specification, a distancebetween any one node and another adjacent node of the support may befrom 10 nm to 500 nm.

According to one embodiment of the present specification, a length fromthe center of the cell to any point of the support may be from 20 nm to500 nm.

According to one embodiment of the present specification, the mixedlayer may include greater than or equal to 10 and less than or equal to400 cells in any region of 1 μm³.

According to one embodiment of the present specification, the mixedlayer may include greater than or equal to 10 and less than or equal to150 cells in any region of 1 μm³.

According to one embodiment of the present specification, the mixedlayer may include greater than or equal to 40 and less than or equal to150 cells in any region of 1 μm³.

According to one embodiment of the present specification, the ionmigration region may be greater than or equal to 40% by volume and lessthan or equal to 85% by volume with respect to the total volume of themixed layer.

According to one embodiment of the present specification, the ionmigration region may be greater than or equal to 40% by volume and lessthan or equal to 80% by volume with respect to the total volume of themixed layer.

According to one embodiment of the present specification, the ionmigration region may be greater than or equal to 40% by volume and lessthan or equal to 70% by volume with respect to the total volume of themixed layer.

According to one embodiment of the present specification, the ionmigration region may be greater than or equal to 40% by volume and lessthan or equal to 60% by volume with respect to the total volume of themixed layer.

According to one embodiment of the present specification, the ionmigration region may be greater than or equal to 40% by volume and lessthan or equal to 55% by volume with respect to the total volume of themixed layer.

According to one embodiment of the present specification, the ionmigration region may be greater than or equal to 45% by volume and lessthan or equal to 65% by volume with respect to the total volume of themixed layer.

According to one embodiment of the present specification, the ionmigration region may be greater than or equal to 45% by volume and lessthan or equal to 60% by volume with respect to the total volume of themixed layer.

The ion migration region in the present specification may mean a regionexcluding a skeleton formed by the support. In addition, the ionmigration region may be a pore region when only the support is present.Moreover, ions may migrate through the ion-conducting material by theion-conducting material being included in the ion migration region.

According to one embodiment of the present specification, the polymerelectrolyte membrane may exhibit excellent ion conductance when theion-conducting material is included within the above-mentioned range inthe ion migration region.

When the ion migration region of the polymer electrolyte membraneaccording to the present specification is greater than or equal to 40%by volume and less than or equal to 85% by volume, sufficient ionconductance may be secured while securing durability of the polymerelectrolyte membrane. In other words, when the ion migration region isless than 40% by volume, durability of the polymer electrolyte membraneis enhanced, however, there is a disadvantage in that sufficient ionconductance is difficult to be secured. Moreover, when the ion migrationregion is greater than 85% by volume, ion conductance of the polymerelectrolyte membrane increases, however, there is a disadvantage in thatdurability is difficult to be secured.

FIGS. 1 and 2 are diagrams showing one region of the surface of apolymer electrolyte membrane according to one embodiment of the presentspecification. Specifically, FIG. 1 is a diagram showing one region ofthe horizontal surface of a polymer electrolyte membrane of the presentspecification, and FIG. 2 is a diagram showing one region of thevertical surface of a polymer electrolyte membrane of the presentspecification. Furthermore, the region expressed as a dark region meansa support, and a light region means an ion migration region.

The vertical surface may mean a surface in the thickness direction ofthe polymer electrolyte membrane. In addition, the horizontal surface isa surface vertical to the thickness direction of the polymer electrolytemembrane, and may mean a surface occupying a relatively large region.

In FIG. 1 and FIG. 2, the ion migration region may mean a cell section,and cells 3 dimensionally bordering the shown cells are present insidethe polymer electrolyte membrane.

The cell of the present specification may have a spherical shape, ashape of pressed sphere, or a polyhedron shape, and when the cell has aspherical shape, the cell section may have a closed figure having aheight to width ratio of 1:1 to 5:1.

When nodes and fibrous branches connecting the nodes of the support areconnected in the cell of the present specification, it may mean avirtual 3-dimensional closed space surrounded by virtual planes formed.The node may mean a site in which two or more fibrous branches meet.Specifically, the node may mean a site in which two or more fibrousbranches meet to form a branching point including 3 or more branches.

FIG. 3 is a diagram showing one region of the section of a polymerelectrolyte membrane according to one embodiment of the presentspecification. Specifically, the dotted region in FIG. 3 is a virtualline, and is to divide a virtual 3-dimensional closed space. Thoseexpressed as a dark region are fibrous branches or nodes of a support,and these are connected 3 dimensionally.

In addition, the cell of the present specification is a unit space of anion migration region including an ion-conducting material surrounded byfibrous branches of the support, and the horizontal and the verticaldirection sections of the virtual 3-dimensional closed space in the caseof being surrounded by the support fibers may have a figure of a circle,an ellipse or a simple closed curve.

In addition, the cell of the present specification means having a volumeof larger than certain sizes, and cells having a diameter of less than40 nm may not be considered as the cell.

The diameter of the cell in the present specification may mean a lengthof the longest line crossing the cell.

One embodiment of the present specification provides a polymerelectrolyte membrane in which the thickness ratio of the mixed layer isgreater than or equal to 30% and less than or equal to 100% with respectto the total thickness of the polymer electrolyte membrane.

According to one embodiment of the present specification, the thicknessratio of the mixed layer with respect to the total thickness of thepolymer electrolyte membrane may be greater than or equal to 50% andless than or equal to 100%.

According to one embodiment of the present specification, the thicknessratio of the mixed layer with respect to the total thickness of thepolymer electrolyte membrane may be greater than or equal to 65% andless than or equal to 95%.

When the thickness ratio of the mixed layer with respect to the totalthickness of the polymer electrolyte membrane is outside theabove-mentioned range and less than 50% with respect to the totalthickness of the polymer electrolyte membrane, a durability enhancingeffect of the mixed layer by the support may be insignificant.Specifically, when the thickness of the mixed layer is less than 50%with respect to the total thickness of the polymer electrolyte membrane,the polymer electrolyte membrane may have reduced durability due to aninfluence of the behavior of a pure layer formed with an ion-conductingmaterial.

According to one embodiment of the present specification, the polymerelectrolyte membrane may be formed only with the mixed layer.Specifically, according to one embodiment of the present specification,when the polymer electrolyte membrane is formed only with the mixedlayer, the thickness ratio of the mixed layer with respect to the totalthickness of the polymer electrolyte membrane may be 100%.

According to one embodiment of the present specification, the thicknessratio of the mixed layer with respect to the total thickness of thepolymer electrolyte membrane may be greater than or equal to 50% andless than 100%. Specifically, according to one embodiment of the presentspecification, the polymer electrolyte membrane may further include apure layer formed with the ion-conducting material on the upper surfaceand/or the lower surface of the mixed layer.

When the polymer electrolyte membrane is formed only with the mixedlayer, joint strength between the polymer electrolyte membrane and anelectrode may be reduced, and this may lead to a problem of theelectrode and the polymer electrolyte membrane being separated whileoperating a fuel cell.

One embodiment of the present specification provides a polymerelectrolyte membrane in which the mixed layer has a thickness of greaterthan or equal to 1 μm and less than or equal to 30 μm.

According to one embodiment of the present specification, the thicknessof the mixed layer may be greater than or equal to 1 μm and less than orequal to 25 μm.

According to one embodiment of the present specification, the thicknessof the mixed layer may be greater than or equal to 1 μm and less than orequal to 15 μm.

According to one embodiment of the present specification, the thicknessof the mixed layer may be greater than or equal to 5 μm and less than orequal to 15 μm.

When the thickness of the mixed layer according to the presentspecification is greater than or equal to 1 μm and less than or equal to30 μm, high ion conductance and durability may be obtained. In addition,when the thickness of the mixed layer is within the above-mentionedrange, durability decline due to a thickness decrease may hardly occur.In other words, when the thickness of the mixed layer is less than 1 μm,there is a disadvantage in that durability is not maintained, and whenthe thickness is greater than 30 μm, there is a disadvantage in that ionconductance may decrease.

According to one embodiment of the present specification, the polymerelectrolyte membrane may be formed only with the mixed layer.

According to one embodiment of the present specification, the polymerelectrolyte membrane may further include a pure layer including only theion-conducting material provided on the upper surface, the lowersurface, or the upper surface and the lower surface of the mixed layer.

According to one embodiment of the present specification, the mixedlayer may be formed by immersing the support into the ion-conductingmaterial.

Specifically, according to one embodiment of the present specification,when the ion-conducting material is included up to the thickness rangeof the support, a polymer electrolyte membrane without a pure layer maybe formed. In addition, according to one embodiment of the presentspecification, when the ion-conducting material is included exceedingthe thickness range of the support, a polymer electrolyte membraneprovided with a pure layer on the upper surface and/or the lower surfaceof the mixed layer may be prepared.

According to one embodiment of the present specification, anion-conducting material included in the mixed layer and anion-conducting material included in the pure layer may be different fromeach other. Specifically, according to one embodiment of the presentspecification, after forming the mixed layer, a pure layer may be formedby coating an ion-conducting material that is different from anion-conducting material included in the mixed layer on the upper surfaceand/or the lower surface of the mixed layer.

According to one embodiment of the present specification, the purelayers provided on any one surface of the mixed layer may be eachindependently laminated in two or more layers, and each layer mayinclude a different ion-conducting material.

According to one embodiment of the present specification, thethicknesses of the pure layers provided on any one surface of the mixedlayer may be each independently greater than 0 μm and less than or equalto 6 μm.

According to one embodiment of the present specification, the purelayers may be each provided on the upper surface and the lower surfaceof the mixed layer.

According to one embodiment of the present specification, the thicknessdifference between the pure layers each provided on the upper surfaceand the lower surface of the mixed layer may be 50% or less of thethickness of the mixed layer. Specifically, the thickness differencebetween the pure layers provided on the upper surface and the lowersurface of the mixed layer may be 30% or less of the thickness of themixed layer. According to one embodiment of the present specification,the thickness difference between the pure layers being 0% of thethickness of the mixed layer means that the thicknesses of the purelayers each provided on the upper surface and the lower surface of themixed layer are the same.

According to one embodiment of the present specification, when thethickness difference between the pure layer provided on the lowersurface of the mixed layer and the pure layer provided on the uppersurface of the mixed layer is 50% or less of the thickness of the mixedlayer, the degree of contraction and expansion of the upper surface andthe lower surface of the polymer electrolyte membrane becomes similareven when humidification and drying of the polymer electrolyte membraneare repeated, and the occurrence of cracks may be prevented.

According to one embodiment of the present specification, the thicknessratio of the mixed layer and the whole pure layer may be from 1:0 to1:4. Specifically, the thickness ratio of the mixed layer and the wholepure layer may be from 1:0 to 1:1.5. More specifically, the thicknessratio of the mixed layer and the whole pure layer may be from 1:0 to1:1.

The polymer electrolyte membrane according to one embodiment of thepresent specification is capable of exhibiting high durability under acondition that humidified and dried states are repeated as the thicknessratio of the mixed layer increases with respect to the pure layer.

According to one embodiment of the present specification, the totalthickness of the polymer electrolyte membrane may be greater than orequal to 3 μm and less than or equal to 36 μm.

According to one embodiment of the present specification, the ionmigration region may include the ion-conducting material in greater thanor equal to 60% by volume and less than or equal to 100% by volume.

According to one embodiment of the present specification, the ionmigration region may include the ion-conducting material in greater thanor equal to 70% by volume and less than or equal to 100% by volume.

According to one embodiment of the present specification, the polymerelectrolyte membrane may have air permeability of 1 hour/100 ml orgreater.

The polymer electrolyte membrane according to one embodiment of thepresent specification may exhibit excellent efficiency in a fuel cell byforming a dense structure. Specifically, the dense structure of thepolymer electrolyte membrane may be shown through the air permeabilityvalue. When the polymer electrolyte membrane according to one embodimentof the present specification has air permeability in the above-mentionedrange, excellent electrolyte membrane performance may be exhibited in afuel cell.

The present specification provides a membrane electrode assemblyincluding the polymer electrolyte membrane. In addition, the presentspecification provides a fuel cell including the membrane electrodeassembly.

The fuel cell of the present specification includes fuel cells generallyknown in the art.

One embodiment of the present specification provides a fuel cellincluding a stack that includes the membrane electrode assembly and aseparator provided between the membrane electrode assemblies; a fuelsupply unit supplying fuel to the stack; and an oxidizer supply unitsupplying an oxidizer to the stack.

FIG. 4 is a diagram showing the structure of a fuel cell according toone embodiment of the present specification, and the fuel cell is formedincluding a stack (60), an oxidizer supply unit (70) and a fuel supplyunit (80).

The stack (200) includes one, two or more of the membrane electrodeassemblies, and when two or more of the membrane electrode assembliesare included, a separator provided therebetween is included.

The separator prevents the membrane electrode assemblies from beingelectrically connected, and performs a role of transferring a fuel andan oxidizer supplied from the outside.

The oxidizer supply unit (70) performs a role of supplying an oxidizerto the stack (60). As the oxidizer, oxygen is typically used, and oxygenor air may be used by being injected with a pump (70).

The fuel supply unit (80) performs a role of supplying a fuel to thestack (60), and may be formed with a fuel tank (81) storing a fuel, anda pump (82) supplying the fuel stored in the fuel tank (81) to the stack(60). As the fuel, a hydrogen or hydrocarbon fuel in a gas or liquidstate may be used, and examples of the hydrocarbon fuel may includemethanol, ethanol, propanol, butanol or natural gas.

MODE FOR DISCLOSURE

Hereinafter, the present specification will be described in detail withreference to examples. However, examples according to the presentspecification may be modified to various other forms, and the scope ofthe present specification is not interpreted to be limited to theexamples described below. Examples in the present specification areprovided in order to more completely describe the present specificationfor those having average knowledge in the art.

Example 1

As an ion-conducting material, an immersion solution was made bydissolving a sulfonated polyether-etherketone-based ion-conductingpolymer in dimethyl sulfoxide (DMSO) to have a concentration of 7 wt %,and then a polypropylene-based support having porosity of approximately70% and a thickness of approximately 15 μm fixed on a frame of 10 cm×10cm was immersed into the immersion solution. After that, the result wasdried for 24 hours in an oven at 80° C., and a polymer electrolytemembrane was prepared. The prepared membrane was acid treated for 24hours in 10% sulfuric acid at 80° C., washed 4 or more times withdistilled water, dried, and then used. The final thickness of thepolymer electrolyte membrane prepared according to Example 1 was from9.7 to 12.2 μm, the thickness of a mixed layer was from 7 μm to 8 μm,the thickness of a pure layer provided on the upper part of the mixedlayer was from 0.7 μm to 1.2 μm, and the thickness of a pure layerprovided on the lower part of the mixed layer was from 2 μm to 3 μm.

Comparative Example 1

A polymer electrolyte membrane was prepared by casting only theimmersion solution used in Example 1 on a glass plate to a thickness of400 μm, and then drying the result for 24 hours in an oven at 80° C. Theprepared polymer electrolyte membrane was treated in the same manner asin Example 1, and then used. Specifically, the polymer electrolytemembrane prepared according to Comparative Example 1 was formed onlywith a pure layer, and the thickness was 20 μm.

Comparative Example 2

A fluorine-based support having porosity of approximately 90% and athickness of approximately 7 μm fixed on a frame of 10 cm×10 cm wasprepared using polytetrafluoroethylene (PTFE). Moreover, thefluorine-based support was immersed into the immersion solution used inExample 1. The preparation process thereafter was progressed in the samemanner as in Example 1. The final thickness of the polymer electrolytemembrane prepared according to Comparative Example 2 was from 23 μm to31 μm, the thickness of a mixed layer was from 5 μm to 10 μm, thethickness of a pure layer provided on the upper part of the mixed layerwas from 16 μm to 18 μm, and the thickness of a pure layer provided onthe lower part of the mixed layer was from 2 μm to 3 μm.

Durability of the polymer electrolyte membranes prepared according toExample 1, Comparative Example 1 and Comparative Example 2 was measuredthrough an RH cycle, and the results are shown in FIG. 6. According toFIG. 6, the x axis means the number of an RH cycle, and the y axisrelates to a hydrogen crossover value allowing the estimation of thedegree of polymer electrolyte membrane damage while the RH cycle isprogressed.

As shown in FIG. 6, it can be seen that polymer electrolyte membranedamage occurred from an early RH cycle and normal operation was not ableto be conducted in the polymer electrolyte membranes according toComparative Examples 1 and 2. Meanwhile, it can be seen that electrolytemembrane damage did not occur even when the RH cycle exceeded 50,000cycles in the polymer electrolyte membrane according to Example 1.

Test Example 1 Evaluation on Tensile Strength of Polymer ElectrolyteMembrane

Tensile strength of the polymer electrolyte membranes prepared accordingto Example 1, and Comparative Examples 1 and 2 was measured.Specifically, the prepared polymer electrolyte membranes were cut into 3pieces each to have an ASTM D-412A dog bone form in the machinedirection and the vertical direction of the machine direction, andtensile strength tests were carried out using a Shimadzu AGS-X 100Napparatus. The tests were carried out with a distance between grips of100 mm and a tension speed of 10 mm/min under a condition of atemperature of 20° C. and a humidity of 22%. The results according toTest Example 1 are shown in the following Table 1.

TABLE 1 Vertical Direction of Machine Direction Machine DirectionMaximum Maximum Maximum Maximum Stress Elongation Stress Elongation(kgf/cm²) (%) (kgf/cm²) (%) Example 1 919.3 72.7 832.7 49.4 1046.5 71.8771.8 35.7 986.1 69 905.6 55 Comparative 672 12.9 702.8 12.5 Example 1673.8 12.3 685.7 6.7 733.1 38.5 692 11.5 Comparative 249.0 2.8 469.610.3 Example 2 308.0 8.6 482.1 8.8 432.4 4.9 373.7 4.1

As seen from Table 1, it can be seen that the polymer electrolytemembrane according to Example 1 had excellent maximum stress and maximumelongation compared to the polymer electrolyte membranes according tothe comparative examples. This indicates that the polymer electrolytemembrane according to one embodiment of the present specification iscapable of exhibiting excellent durability when used in a fuel cell inwhich contraction and expansion are repeated.

Test Example 2 Performance Evaluation of Membrane Electrode AssemblyIncluding Polymer Electrolyte Membrane

In order to measure the performances of the polymer electrolyte membraneprepared in Example 1 in a fuel cell, the polymer electrolyte membranewas cut into a square of 8 cm×8 cm, and a carbon-deposited platinumcatalyst having Pt of 0.4 mg/cm² was transferred in a size of 5 cm×5 cmto the upper surface and the lower surface of the polymer electrolytemembrane, and a membrane-electrode assembly was prepared. Theperformance evaluation was carried out under a condition of 70° C.,relative humidity (RH) of 50%, H₂/Air and atmospheric pressure.

FIG. 7 shows a voltage depending on the current density of the membraneelectrode assembly prepared according to Test Example 2.

As shown in FIG. 7, it can be seen that the voltage decrease dependingon the current density increase was small when the membrane electrodeassembly is used as a fuel cell. This means that excellent performancesare capable of being exhibited when the membrane electrode assembly wasused in a fuel cell.

1. A polymer electrolyte membrane comprising a mixed layer that includesan ion migration region and a support having a 3-dimensional networkstructure, wherein the ion migration region has a structure in which twoor more cells including a hydrocarbon-based ion-conducting materialborder 3 dimensionally, and an RH cycle limit is at least 20,000 cycles.2. A polymer electrolyte membrane comprising a mixed layer that includesan ion migration region and a support having a 3-dimensional networkstructure, wherein the ion migration region has a structure in which twoor more cells including a hydrocarbon-based ion-conducting materialborder 3 dimensionally, and a maximum stress in a machine direction (MD)of the polymer electrolyte membrane is 200 kgf/cm² or greater.
 3. Apolymer electrolyte membrane comprising a mixed layer that includes anion migration region and a support having a 3-dimensional networkstructure, wherein the ion migration region has a structure in which twoor more cells including a hydrocarbon-based ion-conducting materialborder 3 dimensionally, and a maximum stress in a vertical direction ofa machine direction (MD) of the polymer electrolyte membrane is 200kgf/cm² or greater.
 4. The polymer electrolyte membrane of claim 1,which has a maximum elongation in the machine direction (MD) of 20% orgreater.
 5. The polymer electrolyte membrane of claim 1, which has amaximum elongation in the vertical direction of the machine direction(MD) of 10% or greater.
 6. The polymer electrolyte membrane of claim 1,wherein the hydrocarbon-based material is a polymer having one or morecation exchangers on a side chain, a ratio of the number of carbon atomsand the number of fluorine atoms included in the polymer is greater thanor equal to 1:0 and less than 1:1, and the cation exchanger includes oneor more types selected from the group consisting of a sulfonic acidgroup, a carboxylic acid group, a phosphoric acid group, a phosphonicacid group and derivatives thereof.
 7. The polymer electrolyte membraneof claim 1, wherein the ion-conducting material includes one, two ormore types selected from the group consisting of a sulfonatedbenzimidazole polymer, a sulfonated polyimide-based polymer, asulfonated polyetherimide-based polymer, a sulfonatedpolyphenylenesulfide-based polymer, a sulfonated polysulfone-basedpolymer, a sulfonated polyethersulfone-based polymer, a sulfonatedpolyetherketone-based polymer, a sulfonated polyether-etherketone-basedpolymer, a sulfonated polyphenylquinoxaline-based polymer, and a polymerin which a sulfonated partial fluorine-based is introduced.
 8. Thepolymer electrolyte membrane of claim 1, wherein the support includes ahydrocarbon-based material.
 9. The polymer electrolyte membrane of claim1, wherein the support includes a semi-crystalline polymer.
 10. Thepolymer electrolyte membrane of claim 1, wherein the support includespolyolefin, polyamide, polyester, polyacetal (or polyoxymethylene),polysulfide, polyvinyl alcohol, copolymers thereof and combinationsthereof.
 11. The polymer electrolyte membrane of claim 1, wherein theion migration region is greater than or equal to 40% by volume and lessthan or equal to 85% by volume with respect to a total volume of themixed layer.
 12. The polymer electrolyte membrane of claim 1, whereinthe ion migration region includes the ion-conducting material in greaterthan or equal to 60% by volume and less than or equal to 100% by volume.13. The polymer electrolyte membrane of claim 1, wherein a thickness ofthe mixed layer is greater than or equal to 1 μm and less than or equalto 30 μm.
 14. The polymer electrolyte membrane of claim 1, wherein anaverage of maximum diameters of the cells is greater than or equal to0.25 μm and less than or equal to 0.4 μm, and a standard deviation ofmaximum diameters of the cells is greater than or equal to 0.05 μm andless than or equal to 0.2 μm.
 15. The polymer electrolyte membrane ofclaim 1, wherein the cells are laminated in two or more layers in anyone direction (x-axis direction), a direction vertical thereto (y-axisdirection), and a thickness direction of the polymer electrolytemembrane (z-axis direction) from any surface horizontal to an uppersurface of the polymer electrolyte membrane.
 16. The polymer electrolytemembrane of claim 1, wherein the support has a sponge structure in whichtwo or more of the cells are distributed.
 17. The polymer electrolytemembrane of claim 1 comprising sections of two or more of the cells inboth a vertical section and a horizontal section of the polymerelectrolyte membrane.
 18. The polymer electrolyte membrane of claim 1,wherein the support is formed with two or more nodes, and each nodeincludes three or more branches.
 19. The polymer electrolyte membrane ofclaim 1, wherein the mixed layer includes greater than or equal to 10and less than or equal to 400 cells in any region of 1 μm³.
 20. Thepolymer electrolyte membrane of claim 1, which is formed only with themixed layer.
 21. The polymer electrolyte membrane of claim 1 furthercomprising a pure layer including only the ion-conducting materialprovided on an upper surface, a lower surface, or an upper surface and alower surface of the mixed layer.
 22. The polymer electrolyte membraneof claim 1, wherein thicknesses of the pure layers provided on any onesurface of the mixed layer are each independently greater than 0 μm andless than or equal to 6 μm.
 23. The polymer electrolyte membrane ofclaim 1, which has a total thickness of greater than or equal to 3 μmand less than or equal to 36 μm.
 24. The polymer electrolyte membrane ofclaim 1, which has air permeability of 1 hour/100 ml or greater.
 25. Amembrane electrode assembly comprising the polymer electrolyte membraneof claim
 1. 26. A fuel cell comprising the membrane electrode assemblyof claim 25.